Vial
Write to jacksongathondu@gmail.com. Say what you typed and what the app showed, and a person will reply.
Every result is printed beside the expression that produced it. If a number looks wrong, the working is on the same screen, and the full set of expressions is written out on the About screen inside the app.
Open About, or the unlock screen, and tap Restore purchases. That asks the App Store what the Apple ID signed in on this device already holds, and it charges nothing. A Lifetime unlock returns on any device signed in to the same Apple ID. A weekly subscription returns only while it is still active. If it lapsed, restore correctly reports nothing to restore, and that is not a fault of the payment.
In the App Store: your account, then Subscriptions. Cancelling stops the renewal, and the plan runs to the end of the week already paid for. The app has no way to charge you, and no way to cancel on your behalf.
Nothing is deleted. Everything already entered stays on the device and stays readable, and export and import remain free. Only the ability to add beyond one vial or pen is affected.
Open About, export a JSON backup, send it to yourself through the share sheet, then import it on the new device. CSV export is also available, for a spreadsheet rather than a restore. There is no sync: your records are on the device, so a backup is the only way across.
No. Vial does arithmetic on numbers you enter and keeps the record you enter. It offers no doses, no schedules and no drug information, deliberately, and that will not change.
Vial is not medical advice. It makes no claim of diagnosis, treatment, prevention or mitigation, and it is no substitute for the judgement of a qualified professional. Check every figure before acting on it.